When summer’s sun is beating down outside, the inside of your home can quickly become hot and stuffy, with warm, stale air seeming to hang stagnant in every corner. If you’re searching for some alternatives to air conditioning, you might want to consider a whole-house fan. Easy to install, much less expensive to operate than an air conditioner, and surprisingly unobtrusive, a whole-house fan may be all the cooling you need in milder climates, or can offer a great supplement to your other air conditioning on days when it’s not as hot.
Whole-house ventilation fans operate on a very simple principle. The fan unit is mounted in the ceiling in a central location such as a hallway or near the top of the main stairs. Once the outside air temperature drops below the temperature inside, simply open up the windows and flip the switch to activate the fan. The powerful fan motor draws a large volume of cooler outside air into the house, pushing the warmer inside air into the attic and then out through ventilation spaces.
Whole-house fans are not air conditioners, in that they do not actually circulate, process and lower the temperature of the air inside your home. Instead, they cool things down by replacing hot inside air with cooler outside air; by continually flushing hot air out of the attic to reduce ceiling-radiated heat; and by creating a gentle breeze in the house that cools the occupants by an evaporation effect across the skin.
Another advantage of the whole-house fan is its ability to push stale air out of the house and replace it with fresh air, as opposed to simply recycling indoor air through a filter. You’ll even find the whole-house fan is useful during the winter, when you can activate it for a short time on mild days to flush out stale winter odors.
There are two basic types of whole-house ventilation fans: direct-drive and belt-drive. Direct-drive fans have a motor that is attached directly to the fan blades. These are less expensive than belt-drive models, and work fine for small to medium size homes. The primary disadvantages are a higher noise level in the motor, and more vibration in the fan.
Larger fans utilize a belt-drive motor, where the motor is attached above and to the side of the fan and a belt and pulley system is used to turn the fan blades. Belt-drive models are quieter, and the belt and pulley arrangement allows for larger diameter fans with more steeply-pitched blades that can move more air.
Whole-house fans are installed in the attic, and they draw air in through a hole cut in the ceiling. Some fans are designed to sit on top of the ceiling joists, which is an advantage if your house has roof trusses which cannot be cut to create a large opening in the ceiling. Other types – typically the larger units with 30- to 36-inch diameter fans – require that the ceiling joists be cut and framed to create a large, square hole that accommodates the fan box. Complete instructions are provided with the unit, or you may need to consult with a qualified contractor to do the framing.
Inside the house, a louvered cover is mounted to the ceiling to cover the fan. When the fan is activated, the air movement pulls the louvers open, allowing the air to flow into the attic. When the fan is off, the spring-mounted louvers automatically snap back into the closed position, concealing the fan and preventing cold attic air from leaking down during the winter.
Residential whole-house fans operate on 120 volts, and draw between 3.5 and 9 amps. They are typically controlled by a wall-mounted one- or two-speed switch or by a 12-hour timer. Consult with the manufacturer’s instructions or a licensed electrician for complete wiring details.
SIZING THE FAN
Whole-house fans are rated in cubic feet per minute (CFM) of air flow, and need to be sized to the square footage of your home for best cooling results. Most manufacturers recommend that you take the total number of square feet of living space in your home and multiply it by three to determine the size of the fan in CFM. For example, a 1,300-square-foot house would require a fan of approximately 3,900 CFM (1,300 x 3). Larger homes can be served by two fans to provide better air flow and more control over cooling.
The stale air in the attic needs to exit to the outside, so attic ventilation is a very important part of your calculations. Here, the rule of thumb is to divide the capacity of the fan in CFM by 750 to arrive at the total square footage of attic ventilation area needed. For a 3,900 CFM fan, you would need approximately 5.2 square feet of attic ventilation area, which can be any combination of soffit, roof, ridge, and/or gable end vents.
Whole-house fans are available at many home centers, lumberyards, and plumbing and electrical retailers, in stock or by special order.
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